Area formulas of circle

1. Area of a circle = $$\begin{aligned} \pi R^2 \end{aligned}$$ , where R is radius

2. $$\begin{aligned} \text{Circumference of a circle} = 2 \pi R \end{aligned}$$

3. $$\begin{aligned} \text{Length of a arc} = \frac{2 \pi R \theta }{360} \\ \text{ where } \theta \text{ is the central angle } \end{aligned}$$

4.
$$\begin{aligned} \text{Area of sector = } \frac{1}{2}(arc* \theta) \\ = \frac{\pi R^2 \theta}{360} \end{aligned}$$

5.
$$\begin{aligned} \text{Area of a semi circle =} \frac{\pi R^2}{2} \end{aligned}$$

6.
$$\begin{aligned}\text{Circumference of a semi circle =} \pi R \end{aligned}$$